The present invention generally concerns localized microwave distribution systems (LMDS). More particularly, the present invention concerns dynamic downstream and upstream frequency assignment for stations within the communication area of a base station of an LMDS.
Point-to-multipoint localized distribution systems are known in the art. Typical systems use multiple low power node antennas, also commonly referred to as cell stations, base stations, and hub stations, which deliver wireless communication services to receiving stations in an area of coverage, e.g., xe2x80x9ccellxe2x80x9d, defined around the node antennas. The node antennas are arranged to form partially overlapping cells. Frequency differentiation, polarization differentiation and similar techniques are used alone or in combination to prevent conflicting signals from adversely affecting communications received by receiving stations at or near areas of overlap between adjacent node antennas and between adjacent sectors of a particular node antenna.
An interesting point-to-multipoint microwave television distribution system utilizes devices in the millimeter wave frequency band, between about 28 GHz and 300 GHz. Of particular interest is the 29 GHz band, from 27.5 to 31.3 GHz, which provides sufficient width to accommodate a number of broadband channels, avoids previously allocated terrestrial bands, avoids satellite down-link bands, permits relatively small sized antennas, and is compatible with known low-cost microwave circuit fabrication techniques.
In such a LMDS, a low power microwave base station communicates with a plurality of subscriber stations in its transmission cell. Multiple base stations are arranged in an array to extend coverage beyond a single cell. LMDS telephony and data communications from a base station typically communicate with subscriber customer premise equipment located within about 5 kilometers of the LMDS base station. Establishing and maintaining communications with customer premise equipment i.e., all equipment in customer premises connected through the LMDS wireless link, such as RF Network Interface Unit (NIU), telephones, computers, PBXs, etc., requires allocation of channels and time slots for communication of data and control information. Efficient use of available bandwidth is best realized through a dynamic frequency assignment since having fixed frequencies for particular CPE will often leave significant unused bandwidth.
Three general problems are encountered with such dynamic assignment. First, a downstream channel must be dynamically assigned to a customer premises NIU. In addition, an upstream channel and time slot must be dynamically assigned to a customer premises NIU. Finally, a manner for a customer premise to request either downstream or upstream frequency assignment must be provided.
This dynamic LMDS assignment problem remains essentially unaddressed in conventional LMDS. Mobile telephone cellular systems have one or more frequencies dedicated for requesting a downstream control frequency. This dedicated downstream frequency is separate from the data frequencies used to carry voice payload. This approach has little value for LMDS, which is based on assigning a single downstream frequency to a customer premises, with several customer premises sharing the same upstream frequency for control and transferring of telephony and data information. A further difference is that LMDS supports trunk line service while cellular does not. LMDS accordingly has a unique set of requirements for performing both dynamic downstream and upstream frequency assignment, believed to be unaddressed in known prior art techniques.
Thus, there is a need for an improved localized microwave distribution system that provides for dynamic downstream and upstream frequency assignment. It is an object of the present invention to provide such an improved system.
It is a further object of the invention to provide an improved localized microwave distribution system including a method and protocol for dynamically allocating customer premise equipment to a downstream frequency based upon periodic message assignments retrieved through a scan of home common control channels.
An additional object of the invention is to provide an improved localized microwave distribution system including a method and protocol for dynamically allocating customer premise equipment to a downstream frequency via a request for downstream frequency assignment.
Another object of the invention is to provide an improved localized microwave distribution system including a method and protocol for dynamically allocating an upstream frequency and time slot to customer premise equipment.
Still another object of the invention is to provide an improved localized microwave distribution system including a method and frequency contention protocol for competing customer premise equipment to pick a common control channel for communicating either a downstream or upstream frequency request or time slot request to a base station.
A still further object of the invention is to provide an improved method and protocol for upstream burst mode applications which require upstream frequency assignment.
These and other objects are met or exceeded by the method and protocol for downstream and upstream dynamic frequency assignment, and the present contention protocol method for resolving customer premise equipment request frequency contentions. The protocol assumes there is a home common control channel (CCC) associated with each downstream frequency. The CCC contain one or more time slots used to communicate information downstream to customer premise equipment, such as upstream frequency and time slot assignments. The home CCC is equivalent to a broadcast of the CCC to any station listening to the downstream channel.
Downstream frequency may be assigned in accordance with the invention via a periodic broadcast of a frequency assignment table. A base station periodically broadcasts the frequency assignment table over the home CCC in each downstream frequency to designate the customer premise equipment (CPE) assigned to the particular downstream frequency. When a CPE is turned on it scans downstream frequencies until it finds its assigned frequency. A more preferred alternative eliminates the broadcast in favor of a request based assignment. In this approach, a CPE scans for non-video downstream frequency and uses one of the CCC associated with that downstream frequency to send a request for a downstream frequency assignment. The CCC is a shared resource, so a contention, or vie, protocol is used to resolve contentions. The vie protocol includes a modified slotted aloha protocol based on retrying a send over the shared resource at increasingly longer pseudo random times after each failed send.
Upstream assignment of the invention is similar in nature. Assignments may be broadcast periodically, or may be obtained by CPE requests messages to the base over one of the CCCs associated with its upstream frequency using the vie protocol. Additional time slots for a CPE having a time slot are requested over that CPE""s assigned CCC frequency using the vie protocol.